Why Do Some Sections of Sidewalk Have Bumps?

It’s easy for some pedestrians to go their whole lives without paying much attention to the raised bumps that cover parts of the sidewalk they step on. But for others, those little dots are essential to getting around.

In this video spotted by Tom McParland of Jalopnik, video producer Tom Scott explains the ingenious purpose behind this piece of infrastructure. Blistered sections of pavement can communicate important messages to visually impaired pedestrians. A uniform grid of circles signals a sloping curb leading to a crosswalk. If the squares are red, that indicates to a partially sighted person that the path has a light for stopping traffic.

Varying patterns symbolize specific hazards. Strips of offset bumps, for example, are usually placed at the edge of a subway platform. And as Scott lays out in the video above, pill-shaped bumps and striped patterns are used to alert pedestrians to completely different situations.

Tactile paving was first introduced in Japan in 1967 [PDF], and the infrastructure trick has since spread to countries around the world. In the United States, the warnings are required by the Americans With Disabilities Act for public transportation facilities and other areas covered by the ADA.

Could an Astronaut Steal a Rocket and Lift Off, Without Mission Control?

Not with any rocket that has ever thus far carried a person into orbit from Earth, no. Large rockets are complex, their launch facilities are complex, their trajectories are complex, and the production of their propellants is complex.

Let me give you one simple example:

Let’s say astro-Sally is the last woman on Earth, and is fully qualified to fly the Saturn-V.

Further, let’s say the Rapture (which as I understand it, is some sort of hip-hop induced global catastrophe that liquefies all the people) has left a Saturn-V sitting on the pad, raring to go.

Further, let’s grant that, given enough time, astro-Sally can locate sufficient documentation to operate the several dozen controls needed to pump the first stage propellant tanks full of kerosene.

Now what? Oxidizer, right? Wrong. First, she has to attend to the batteries, oxygen, hydrogen, and helium pressurant tanks in her spacecraft, otherwise it’s going to be a short, final flight. And she’ll need to fill the hypergolics for the spacecraft propulsion and maneuvering systems. If she screws that up, the rocket will explode with her crawling on it. If she gets a single drop of either of these on her skin or in her lungs, she’ll die.

But okay, maybe all the hypergolics were already loaded (not safe, but possible) and assume she manages to get the LOX, H2, and HE tanks ready without going Hindenburg all over the Cape.

And…let’s just say Hermione Granger comes back from the Rapture to work that obscure spell, propellantus preparum.

All set, right? Well, no. See, before any large rocket can lift off, the water quench system must be in operation. Lift off without it, and the sound pressure generated by the engines will bounce off the pad, cave in the first stage, and cause 36 stories of rocket to go “boom.”

So she searches the blockhouse and figures out how to turn on the water quench system, then hops in the director’s Tesla (why not?) and speeds out to the pad, jumps in the lift, starts up the gantry—and the water quench system runs out of water ... Where’d she think that water comes from? Fairies? No, it comes from a water tower—loaded with an ample supply for a couple of launch attempts. Then it must be refilled.

Now imagine how much harder this would all be with the FBI on your tail.

Can a rocket be built that’s simple enough and automated enough to be susceptible to theft? Sure. Have we done so? Nope. The Soyuz is probably the closest—being highly derived from an ICBM designed to be “easy” to launch, but even it’s really not very close.

What Causes Red Tides?

Every once in a while, the ocean turns the color of blood and scores of dead fish rise to the surface. The phenomenon might look like a biblical plague, but the source is far more mundane. It's just algae.

Red tides occur when there’s a sudden population boom among specific kinds of algae, which in enormous quantities become visible to the naked eye. They occur all over the world. In the Gulf of Mexico, the culprit behind red tides washing onto coastlines from Texas to Florida is usually a type of microscopic algae called Karenia brevis. It produces toxic chemicals that can cause symptoms ranging from sneezing and eye irritation to disorientation, vomiting, and breathing difficulties. It's often fatal for fish, shellfish, turtles, and other wildlife.

The water appears red because of the particular depth at which the algae live. Light waves don’t penetrate seawater evenly, and certain wavelengths travel farther than others. The algae that cause red tides grow at depths that absorb green and blue frequencies of light and reflect red ones.

Not all algal blooms are red; some are blue, green, brown, or even purple. Nor do all algae harm humans or animals. Why and how certain species of algae multiply like crazy and wipe out entire swaths of marine life is still a scientific mystery.

The worst red tide on record occurred in 1946, when a mass of algae stretching for 150 miles along the Florida coastline killed more than 50 million fish, along with hundreds of dolphins and sea turtles. Tourists shied away from the beaches as the bodies of dead sea creatures washed ashore. Smaller incidents are more common, but just as costly. In the past decade alone, fishing and tourism industries in the United States have had an estimated $1 billion in losses due to red tides—and the cost is expected to rise.

Editor's note: This story, which originally ran in 2015, was updated in August 2018.